Jethro Tull's Ian Anderson at Sands Bethlehem Event Center isn't living in the past. Should he be?

It’s hard to figure what to make of progressive rock these days – at least the progressive rock of Jethro Tull lead singer Ian Anderson, who performed Sunday at Sands Bethlehem Event Center.

On one hand, its complexity and sheer musicality makes it stand far apart from senseless drivel such as Taylor Swift’s new album. And Anderson’s particularly theatrical style of presenting it made it instantly intriguing.

On the other hand, Anderson’s material from his new album “Homo Erraticus,” released in May, was presented so theatrically, that it very much seemed more a play than music able to stand on its own, except that it had no discernible story, or even message.

And the older songs that Anderson billed as “the best of Jethro Tull,” while still impressive, sounded a bit tattered as played Sunday, and dipped into cover-band territory when – despite the fact Anderson was on stage – some were largely sung by a different vocalist.

The show was offered in two sets, with the first hour containing seven songs of the 15 from ”Homo Erraticus” then a couple of Tull hits, and the second hour 10 of the supposed best of Tull.

The new songs were very much a stage presentation, with a video introduction of the 67-year-old Anderson as an Alzheimer’s patient offering the introduction, “Thought I was a gonner, did you?” and members of his four-man band (all of whom have played in configurations of Jethro Tull) coming out in medical white coats.

And Anderson gave his typical theatrical performance – by the middle of the first song, the “Homo Erraticus” opening tune “Doggerland,” he was standing on one leg to play the flute.

The new songs were undistinguished – and undistinguishable, seeming more like the background music that moves along the plot of a play than stand-alone songs. Trouble was, if there was a play or message they were telling, it was indiscernible – either too esoteric or poorly conveyed, with the lyrics not understandable.

But it all sounded ominous and seemed like important stuff: During “Enter the Uninvited,” the video screen flashed images of “Star Trek” and “The Walking Dead.” On “Puer Ferox Adventurus,” a grim reaper character swept the floor. On “The Browning of the Green, backup singer Ryan O’Donnell walked around in a lab coat with a clipboard.

And on the disc’s closing song, “Cold Dead Reckoning,” the screen flashed images of Muammar Gaddafi, Saddam Hussein, Adolf Hitler … and George W. Bush (really?) before ending with two blasts of light.

The nearly full audience of something more than 2,000 seemed genuinely interested, but it wasn’t until the end of the set, when Anderson played the early Jethro Tull instrumental “Bouree” that they seemed to come alive, clapping along and cheering as Anderson skipped across the stage.

And the first-set-closing “Thick As a Brick” (all of Part I and a snippet of Part II, totaling 16 minutes) got cheers from the opening notes.

The difference, of course, was that song is a classic. But it also has a distinctive melody missing from much of the new music. Yes, the better of Jethro Tull’s songs are now 45 years old, but the reason they still get the reaction they do is because they are good.

But it was disconcerting that O’Donnell sang a sizable chunk of the song, as he did on several other of the “best of” offerings, including the second-set opening “Living in the Past.”

That was especially because Anderson’s voice, while its range shorter and its richness thinner, was nonetheless the distinctive sound of the songs. Anderson duetted with O’Donnell on “With You There to Help Me” from the 1970 album “Benefit,” but the backup singer did at least half of “Too Old to Rock ‘n’ Roll, Too Young to Die” and “Farm on the Freeway.”

The other disappointment is that those songs, as well as “Critique Oblique” from “A Passion Play,” hardly make up “the best of” Jethro Tull as the concert’s title suggested.

When introducing “Teacher,” which actually is a “best of” song, Anderson suggested he was doing it against his will and had O’Donnell sing most of it. But it’s a song that holds up well – some of Tull’s material doesn’t – and got a loud cheer.

Anderson skipped such gems such as “Bungle in the Jungle,” "Cross-Eyed Mary" and “Skating Away on the Thin Ice of a New Day.”

The show’s main set closed with a nine-minute version of Tull’s “Aqualung,” unquestionably Jethro Tull’s greatest song. It holds up as an important song, but it was inexcusable that O’Donnell sang so much of it. Without Anderson, it came too close to a tribute band – which, without him, it was.

Despite that, the audience rushed the stage and gave a standing ovation to the band, which returned for a nine-minute encore of “Locomotive Breath” that was strong and strongly played.

That, honestly is what made prog rock so enticing – its strong musicality, but also its connection to rock and roll. The theatrics might have been something special to Jethro Tull, but they didn’t overshadow the music.